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    <p>Just change the first line to:</p> <pre><code>__block MyVideoPlayer *videoPlayer = [[[MyVideoPlayer alloc] init] autorelease]; </code></pre> <p>The reason this works is because:</p> <blockquote> <p>In a reference-counted environment, by default when you reference an Objective-C object within a block, it is retained. This is true even if you simply reference an instance variable of the object. Object <strong>variables marked with</strong> the <strong>__block</strong> storage type modifier, however, <strong>are not retained</strong>.</p> </blockquote> <p>See Apple's Documentation on <a href="https://developer.apple.com/library/ios/documentation/cocoa/Conceptual/Blocks/Articles/bxVariables.html#//apple_ref/doc/uid/TP40007502-CH6-SW3" rel="nofollow">Object and Block Variables</a></p> <h2>But Why Wasn't It Being Released To Begin With?</h2> <p>Simple explanation is that after the <code>completionBlock</code> executes, it is not being released. It is being released later in <code>dealloc</code>, thus all the variables it is retaining are still retained. This makes sense since it is possible to execute a block as many times as you wish until it is released. </p> <p>I've seen this behavior before where an object that owns a block is referenced in the block and releases the block in dealloc, which prevents the object from ever being released. <strong>The solution is to weakly reference the object that owns the block.</strong> This way the owning type, like <code>MyVideoPlayer</code>, reaches <code>dealloc</code>, which subsequently releases the block (<code>completionBlock</code> in this example).</p> <p>An alternative to using the <code>__block</code> keyword to avoid retaining a type is to wrap the object in an <a href="https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/nsvalue_Class/Reference/Reference.html" rel="nofollow"><code>NSValue</code></a> by using the <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/nsvalue_Class/Reference/Reference.html#//apple_ref/doc/uid/20000177-valueWithNonretainedObject_" rel="nofollow"><code>valueWithNonretainedObject:</code></a> and <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/nsvalue_Class/Reference/Reference.html#//apple_ref/doc/uid/20000177-nonretainedObjectValue" rel="nofollow"><code>nonretainedObjectValue</code></a> methods. For instance:</p> <pre><code>MyVideoPlayer *videoPlayer = [[[MyVideoPlayer alloc] init] autorelease]; NSValue *videoPlayerRef = [NSValue valueWithNonretainedObject:videoPlayer]; [videoPlayer canPlayAsset:(MyVideoAsset *)asset completionBlock:^(BOOL isAssetPlayable) { if (isAssetPlayable) { MyVideoPlayer *tempVideoPlayer = (MyVideoPlayer*)[videoPlayerRef nonretainedObjectValue]; [tempVideoPlayer playAsset:asset]; [self presentModalViewController:tempVideoPlayer animated:YES]; } }]; </code></pre> <h2>Edit / Conversation</h2> <p>This section is to expand further into why the block is not being released. I am going to include what I assume is happening behind <code>MyVideoPlayer</code>. It would be great to see actual code, but this should suffice.</p> <p><strong>Header file...</strong></p> <pre><code>typedef void(^MyVideoPlayerCompletionBlock)(BOOL isAssetPlayable); @interface MyVideoPlayer : NSObject @property(nonatomic, copy) MyVideoPlayerCompletionBlock completion; ... // other property definitions (or ivars) -(void)canPlayAsset:(MyVideoAsset*)asset completionBlock:(MyVideoPlayerCompletionBlock)completion; ... // other methods defined @end </code></pre> <p><strong>Implementation...</strong></p> <pre><code>@implementation MyVideoPlayer @synthesize completion = _completion; -(void)dealloc { // Note: Block is released in dealloc like any other property or variable [_completion release], _completion = nil; ... // other variables and properties not shown here are released [super dealloc]; } -(void)canPlayAsset:(MyVideoAsset*)asset completionBlock:(MyVideoPlayerCompletionBlock)completion { ... // Does something with asset. Plays it, stores it, whatever // Saves completion block to call at a later time. // Note that this code could alternatively look like // _completion = [completion copy]; // Blocks are usually copied and not retained self.completion = completion; } </code></pre> <p><strong>... AT SOME POINT THE COMPLETION BLOCK FIRES ...</strong> <em>(probably in an event handler or some sort)</em></p> <pre><code>-(void)SomeEventHandlerOrFuncThatCallsCompletionInMyVideoPlayer { // Time to call completion! if (self.completion) { self.completion(YES); // OR no, doesn't matter // // WHOA! :: self.completion is not released // // i.e. self.completion is not nil, and all // variables inside it are still retained // because calling a block doesn't also // release the block. To do that you would // need to do: self.completion = nil; // AFTER calling: self.completion(...); // // SO... // // Because the block was not released, it is // still retaining variables (such as the current // instance of MyViewPlayer). Note that the // Block will never be released until dealloc // is called. :( So..., if you want the block // to retain the current MyViewPlayer until // execution of the completion block is over, you // will want to call: self.completion = nil; // to release the block and all associated variables // after calling the completion block. } } @end </code></pre>
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    1. POCan someone explain why this Block leaks?
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    1. COIf I use __block then the videoPlayer could be released before it has been determined that the asset can play. The block actually does need to retain the videoPlayer.
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      1. USJose Ibanez
    2. CO@Joe This is a tricky situation... If the block retains the `videoPlayer` (+1 retain count) and then releases the object inside the block (0 retain count), it should fire it's `dealloc` method that I assume releases the block, which should cause `videoPlayer` to be released again (-1 retain count). The imbalance comes from the release in the code wrapped in the block... If you own the `MyVideoPlayer` type, you could try releasing the `completionBlock` as soon as it finishes executing. That might work without needing to call release inside the block.
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    3. COOk, I guess that was my question. Why isn't the block being released when the `canPlayAsset:completionBlock:` finishes executing? Shouldn't a literal block declaration like that behave like an autoreleased object?
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